I've been rolling so well on roll20 lately that I suspect their RNG is broken. I crit a player four times in one combat few sessions back, and I recently rolled this:
2d20, result: 20, 20
2d6, result: 6, 6
2d6, result: 6, 5
2d6, result: 6, 5
All in one roll. And yes, that's a Vorpal...